The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.
Not applicable.
(1) Field Of The Invention
The present invention generally relates to a sonar array, and more particularly to a three dimensional array of sonar sensors.
(2) Description of the Prior Art
Arrayed transducers are known in the art. Specifically, Hill et al., U.S. Pat. No. 4,380,808, describes a sparse or xe2x80x9cthinnedxe2x80x9darray of mass loaded PZT elements. Hill et al. further describes a particular uniform element placement scheme that is utilized to achieve three half-wave element spacings for three separate operating frequencies. Francis, U.S. Pat. No. 4,638,468, describes a polymer hydrophone array with printed circuit wiring. Ehrlich et al., U.S. Pat. No. 4,766,575, describes a cylindrical sonar array that employs rectangular planar array segments that extend in the axial direction when assembled on a cylindrical conducting plate having flat longitudinal portions to which the planar array segments are attached. Each planar array segment comprises two columns of planar transducer elements with each column extending in the axial direction of the cylinder. Peloquin, U.S. Pat. No. 5,550,791 describes a composite hydrophone array assembly that is made from a compliant mandrel such as a hollow tube and at least one wrap of piezoelectric film adhered to the compliant hollow tube at a plurality of locations thereon. Lindberg, U.S. Pat. No. 5,530,683, describes an acoustic transducer that is constructed as a stacked configuration of multi-layer transducer elements. Each layer within the transducer contains elements in (along) one-dimension. Furthermore, the transducer elements are limited to high-frequency operation.
What is needed is a sonar array system that provides a relatively greater spatial operational capability than the prior art, and provides single or double resonance frequency elements.
The present invention is directed to a three-dimensional array of acoustic sensors for underwater imaging applications. The array utilizes electroplated layers of piezoelectric polymer (PVDF), or any other electrostrictive polymer, in conjunction with interleaved circuit support layers to providing a volumetric three-dimensional array whereby individual transducer elements may be formed between parallel circuit support layer layers. The three-dimensional configuration of transducers allows formation of acoustic beams in any direction. The individual transducer elements can be grouped into logical transducers operating in a different frequency band. The array can be used for both transmitting and receiving.
The sonar array of the present invention has many applications, e.g., smart acoustic countermeasure devices and unmanned underwater vehicle SONAR systems. The three-dimensional array elements provide a SONAR user with a relatively increased operational field of view as compared to prior art two-dimensional arrays.
A feature of the array of present invention is the use of piezoelectric or electrostrictive polymers (i.e. PVDF) as an active transduction material. An advantage of this feature is that the specific acoustic impedance of piezoelectric polymer is very closely matched to that of water. When the acoustic impedance of the array elements of the volumetric array of the present invention are closely matched to the surrounding fluid (e.g., ocean water), transmission and reception of very wide-band acoustic signals can be realized.
Another important feature of the present invention is that the array can be configured to have a planar or cylindrical geometry.
In one aspect, the present invention is directed to a sonar array comprising a transducer element having a plurality of layers of acoustically transparent electro-acoustic transducer material in a laminated configuration. Each of the layers has a first side with a plurality of electrically conductive portions that are (i) electrically isolated from each other, (ii) arranged in a two-dimensional arrangement, and (iii) configured to have a first polarization. The second side has a plurality of electrically conductive portions that are (i) electrically isolated from each other and the conductive portions on the first side, (ii) arranged in a two-dimensional arrangement that is the same as the two-dimensional arrangement in which the conductive portions of the first side are arranged such that the conductive portions of the second side are substantially aligned with the conductive portions of the first side, and (iii) configured to have a second polarization opposite the first polarization. The layers are arranged so that opposite polarizations do not confront each other. The end layers of the laminated configuration have exposed sides which have different polarities. The electrically conductive first side portions corresponding to the same location within the two-dimensional arrangement are electrically connected together and the electrically conductive second side portions that correspond to the same location within the two-dimensional arrangement are also electrically connected together.
The sonar array can also have a pair of circuit support layers attached to a corresponding exposed side. Each of the circuit support layers has a plurality of electrically conductive regions that are electrically isolated from each other. Each of the regions is electrically connected to a corresponding electrically conductive portion of the exposed side. A plurality of electrically conductive terminal members are attached to each circuit support layer and electrically connected to a corresponding region.
In a preferred embodiment, the acoustically transparent electro-acoustic transducer material is selected from the group consisting of urethane, electrostrictive polyurethane, polyvinylidene fluoride, and polyvinylidene trifluoroethylene.